This proposal has two main objectives. First we will explore in detail those properties of the cyclic AMP system which are common to cultured epithelial cells. These studies will elucidate the mechanisms underlying the requirement for 1-methyl-3-isobutylxanthine in order to observe significant stimulation of adenylate cyclase in intact cells, the very stringent control of the hormonal response, the decreased basal and stimulated cyclic AMP levels with increasing epithelial cell density, and the ability of low levels of phentolamine to significantly enhance hormonal stimulation. Secondly, we will compare the cyclic AMP metabolism of normal and neoplastic epithelial cells and explore the relevancy of aberrations in its metabolism to the establishment or perpetuation of the malignant state. In particular we will determine why chemically transformed epithelial cells have lower cyclic nucleotide phosphodiesterase activity, and have lost adenylate cyclase hormonal responsiveness. Also we will compare and contrast adenylate cyclase, cyclic nucleotide phoshodiesterase and protein kinase activities in normal, malignant and very malignant human kidney epithelial cells. Finally, using a transformation phenotype temperature sensitive mutant of a chemically transformed epithelial cell, and mutants of normal epithelial cells resistant to 8-chloro cyclic AMP we will determine if defects in the cyclic AMP system can initiate or perpetuate the neoplastic state.